The invention relates to a control device for the liquid stream suction sYstems used in dentistry. In suction systems of the type in question, where evacuated fluids are drawn into a stream of liquid, the liquid most widely utilized is water from the domestic main. During normal operation, water is drawn into the impeller of a pump set in rotation by an electric motor; however, it happens in such systems that if no water enters the system, or even if the pressure of the water supply is simply too low, the pump will deteriorate rapidly.
This being the case, the system will generally be provided with a pressure switch designed to sense the pressure level of the water supply, and in the event of the level falling below a given threshold, to generate a signal that switches off the system; in most instances, such a switch will operate by cutting off the electrical power supply to the motor and actuating a solenoid valve to close the water supply inlet.
One of the disadvantages of these systems is that the opening movement of the solenoid valve induces hammering in the water supply line, setting up pressure waves that are picked up by the pressure switch and have the effect of triggering a rapid succession of on and off movements during the transition from standstill to normal operation of the suction circuit. The result is that one has a deterioration of the various components producing electrical contact, due to the surges in current that accompany the rapidly alternating on and off movements preceding steady operation.
Hammering-induced pressure waves also occur in the event of a sudden drop or cut in the electrical power supply; furthermore, critical pressure levels in the water supply itself can cause the entire system to vibrate.
The object of the invention is to overcome the drawbacks described above by providing a control device which will shut off the suction system in the event that water supply pressure should either become insufficient or fail altogether, and at the same time, remain unaffected by sudden variations in pump inlet pressure, in particular when produced by hammering.